Reset Normals directions to object rotation after applyed scale
Are you in object mode or edit mode? Either way, applying rotation resets the orientation of the object.  But what you can do (and this is better) is use the 3D cursor tool to snap the 3D cursor to the geometry, and use 3D cursor transform orientation. You can create an empty with the 3D cursor's rotation and create a custom transform orientation, too. It will create the orientation from whatever is the active selection.